when a large “without contact” zone is encountered. The increase
in the length of a continuous “without contact” zone,
which is not interrupted by “with contact” zones, may considerably
reduce the natural frequencies. Also, it changes the mode
shapes to have local deformation at the debonded region rather
than global deformation.
- A real contact condition model has been developed to evaluate
dynamic response of a debonded beam. Natural frequencies can
be obtained by applying the FFT to the beam's dynamic response
evaluated by the real contact model. Comparing frequencies
obtained by the real contact condition with linear model justifies
using the “with contact” model.
- In a curved beam with circumferentially free ends, increase in
curvature angle slowly decreases the natural frequencies.
When the boundaries are fixed against movements in this direction,
however, the frequencies of the symmetric modes
remarkably increase with curvature angle, while the asymmetric
modes slowly decrease. In this way, the sequences of
modes are changed at specific angles, namely the mode
switching points.
- In beams with free ends, the effect of debonding is identical for
beams with different curvature angles. When the boundaries
are fixed against the circumferential movements, a change in
curvature angle may slightly increase or decrease the effect of
debonding.
- The debonding has minor effect in small debonded region. As it
is expected the increase in debond length decreases the frequencies.
For instance, a debonded region of one third of the
beam length can reduce the frequencies up to 20%.
- The debonding does not influence all modes in a similar way
and it depends on the position of the debonded region. If the
debonded area is located where the core's shear stress is high
in a certain mode, it has a more prominent effect on that
mode